Uptake of sulfolane and diisopropanolamine (DIPA) by cattails (Typha latifolia)

Sulfolane (tetrahydrothiophene 1,1-dioxide, C4H8O2S) and diisopropanolamine (DIPA) are highly water-soluble organic compounds used in the Sulfinol™ process to remove hydrogen sulfide from natural gas and have been found in samples of wetland vegetation collected near a sour gas processing facility in Alberta, Canada. Concentrations within individual plants and between plants at different locations within the wetland varied greatly but were generally higher than expected, based on exposure concentrations and plant uptake predictions using octanol/water partition coefficients. To better understand the uptake of these highly water-soluble compounds by wetland plants and to substantiate the field findings, the uptake of sulfolane and DIPA by cattails (Typha latifolia) was investigated in a greenhouse microcosm study. Cattails were grown hydroponically in aqueous solutions containing sulfolane and DIPA for a period of 50 days. Non-planted and non-planted poisoned hydroponic systems were run simultaneously as controls. Sulfolane and DIPA concentrations in the hydroponic solution and plant tissues were monitored throughout the study. Uptake and translocation of sulfolane and DIPA by cattails were found to be a function of exposure concentration and water transpired. However, the neutral sulfolane was translocated into the foliar portion of the cattails to a significantly greater extent than the protonated DIPA. Sulfolane concentrations were consistently greatest in the leaf tips with concentrations as high as 33,000 mg/kg dry weight for the 200 mg/L exposure. DIPA leaf concentrations were more uniform but much lower than sulfolane. The highest DIPA concentration observed was 1014 mg/kg dry weight for the 100 mg/L exposure. The average leaf to root tissue concentration ratio for sulfolane was 53 (152 for leaf tips), while for DIPA the ratio was 0.6. Normalizing the leaf concentration in each system to the amount of water transpired during exposure and dividing it by the average exposure concentration yielded approximate transpiration stream concentration factors (TSCF) that ranged from 0.1 (entire leaf) to 0.9 (leaf tip) for sulfolane and < 0.01 to 0.02 for DIPA. Overall, the laboratory uptake trends matched those observed in the limited field sampling and suggest that the uptake of non-ionizable, highly water-soluble organics such as sulfolane may not be well predicted using existing relationships between TSCF and log Kow. In addition, the relatively high concentrations observed in the foliar tissue suggest that wetland plants could play an important role in the natural attenuation of sulfolane, provided the sulfolane is not released by the plants during winter dormancy.